In the papermaking process a wide variety of equipment is used, such as Fourdrinier screens and various rolls, such as cylinder rolls and dandy rolls covered with a wire mesh screen or woven fabric. Such screens have customarily been fabricated of metallic filaments and for installation on a supporting structure, the opposite ends of the fabric have been seamed by sewing or brazing with precious metal alloys. In using such brazing techniques great care is required in applying the braze so that the uniform porosity inherent in the wire fabric cloth will not be disrupted. In recent years metallic wire cloth used in papermaking industry is being displaced by thermoplastic monofilament screens. As a consequence, patching and seaming procedures heretofore used in the industry are no longer suitable for use on these synthetic plastic fabrics and new techniques are being sought after.
It is the principal object of this invention to provide methods and means for patching and seaming thermoplastic monofilament fabric using ultrasonic welding techniques.
It is a further object of this invention to provide method and means for ultrasonic welding in such a way that the uniform porosity of the monofilament fabric is maintained in the weld zone in both the overlap or butt seams.
Another object of this invention is to provide ultrasonic welding apparatus for efficiently and economically carrying out the methods embodying this invention.
A still further object of this invention is to provide accessory apparatus for patching and seaming thermoplastic fabric using an ultrasonic welding implement.
Yet another object of this invention is to provide a method for butt seaming the ends of a thermoplastic fabric using ultrasonic welding, wherein the problem of thermoplastic filament distortion from the welding operation is substantially eliminated.